The present invention relates to an electronic device which can be energized from one of a plurality of power sources, including a battery or the like built in it and an external power source, such as an AC adapter, and an external battery, and in particular to an electronic device capable of detecting a voltage input through a power source connector and finding which of the AC adapter, external battery and the like is being connected, and controlling consumption of power depending on which power sources the electronic device is being energized.
FIG. 6 is a perspective view from the rear side of a notebook-type personal computer in the prior art. The personal computer comprises a main unit 20, provided with a dedicated DC-IN (AC adapter) connector 21, and a dedicated external battery connector terminal 22. For connection with an AC adapter, the DC-IN connector 21 is used, while for connection with an external battery, the external battery connector 22 is used.
FIG. 7 is a block diagram showing a power supply circuit in the prior art, which is shown for example in Japanese Patent Kokoku Publication No. 16625/1981, for energizing an electronic device, in particular an electronic device main circuit 78. A connector 71 is provided on the electronic device for connection with an external power source, such as an AC adapter, an external battery or a car battery, via a plug, not shown, connected to the external power source.
The connector 71 has terminals 71a, 71b, 71c and 71d. A switch 77 is opened when a magnetic relay 76 is energized. On the basis of the state of connection of the four terminals 71a, 71b, 71c and 71d, or the state of power source, a power source switch 75, a selecting switch 73, a switch 77 are controlled, so as to energize the electronic device main circuit 78 from the externally connected power source and to charge a built-in battery 74 when the AC adapter is connected.
The electronic device shown in FIG. 6 is provided with separate connectors for the AC adapter input and external battery input, so that the area required for providing the connectors and the number of parts are both considerable.
With the power source device shown in FIG. 7, the connector can be shared, but the number of terminals used in the connector is increased, and it is necessary to detect connection of each of the terminals, and the state of each of switches. The circuit for such detection is complex.
Techniques for sharing a connector is also shown in Japanese Utility Model Kokai Publications No. 121344/1981, No. 141590/1983, No. 70998/1985, No. 90782/1985, and No. 185235/1986. However, these publications do not disclose identifying the type of the power source connected to the common connector, and controlling the internal processing depending on the result of the identification.